1. Field of the Invention
The present invention relates to an illumination control device suitably used for controlling a plurality of light sources mounted on, for example, a vehicle.
2. Description of the Related Art
In a vehicle such as a passenger car, a plurality of portions inside the vehicle cabin may be lighted, a surrounding portion of a door may be lighted when the door is opened/closed, various on-board equipment may be lighted, and illuminating for decoration may be performed in some cases. Accordingly, it is necessary to respectively control a large number of light sources in a vehicle. Besides, it is possible to use a full-color LED device including a plurality of light emitting diodes (LEDs) each emitting light of a wavelength of red (R), green (G) or blue B for adjusting the chromaticity of illumination light in accordance with the situation, or for controlling the illuminating for obtaining various decorative effects. If such a large number of light sources are to be complicatedly controlled, it is preferable to perform centralized control by providing a main control unit for comprehensively controlling the whole illuminating system.
On the other hand, as a related art, for example, JP-A-2000-260575 discloses an illumination control system. JP-A-2000-260575 describes an illumination control system in which the amount of data transferred when a host computer carries out pattern control of control terminals is small and the communication load is small. Specifically, lighting patterns for switching “all turned on”, “all turned off” and “half turned on” are assigned as shown in Table 1 of JP-A-2000-260575.
Besides, an illumination device disclosed in JP-A-2013-120748 employs a technique to reduce wasteful power consumption. Specifically, it is described that a remote controller derives a lighting pattern of each LED on the basis of a distance value, input thereto, between the illumination device and an object.
As a specific example, it is assumed that a control system includes one main control unit and seven sub control units, that each of the seven sub control units includes six output ports, and that the output ports are respectively connected to different light sources. In this case, there are forty-two (6×7) output ports in the whole system, and hence, forty-two light sources can be individually controlled to be, for example, turned on/off. Here, assuming that 1-byte (8-bit) data is transmitted for individually controlling the lighting, extinction, brightness and the like of each of the forty-two light sources based on an instruction from the main control unit, in order to change the controlled states of all the forty-two light sources, it is necessary to transmit, per control, 42-byte data as a whole from the main control unit to each of the sub control units.
Besides, if it is assumed, for example, that the light amount for fade-in/fade-out in turning on/off illumination is to be smoothly changed, it is necessary to repeatedly perform lighting modulation control for each light source at short time intervals. In other words, it is necessary to transmit data from the main control unit to each of the sub control units so as to update the 42-byte data repeatedly at short time intervals.
If a transmission path connecting the main control unit to each of the sub control units has a low data transmission rate, however, it is impossible to transmit the 42-byte data in a short period of time, and hence, control delay may be caused, or the lighting modulation control for the fade-in/fade-out cannot be precisely performed.
Actually, in a system used for purpose of illumination or the like on a vehicle, it is desired to lower the transmission rate of a communication line in order to prevent malfunction derived from an external noise or to reduce device cost. Accordingly, in the above-described control system mounted on a vehicle, it is necessary to reduce the amount of data to be transmitted per control from the main control unit to each sub control unit, or to reduce the number of times of performing transmission.